Magnetic particles (MPs) have received a great deal of interest because of their potential use in various biomedical applications requiring magnetism, such as magnetic resonance imaging. Recent advances in synthesis have enabled the size and shape control of MPs for applications in catalysis and bioimaging. On the other hand, quantum dots (QDs) are emerging as potential biomarkers and have been revolutionising the field of bioimaging in recent years.
Most MPs and QDs are synthesised in organic solvents using hydrophobic surfactants. The resulting nanoparticles are only dispersible in organic solvents i.e. they are hydrophobic. In order to use these particles for biomedical applications, they have to be dispersible in aqueous media and buffer media i.e. they need to be hydrophilic. Different coating strategies exist in the literature to impart the QDs and MPs with hydrophilicity and colloidal stability. Apart from small molecule coatings (e.g. thiols and carboxylic acids), silica and polymer coatings dominate the surface functionalisation methods.
Magnetic resonance imaging (MRI) is regarded as a powerful tool in medicine because of its spatial resolution and its capability to enhance contrast differences between healthy and pathological tissues. However, its low signal sensitivity is a major problem. The combination of MRI and fluorescence imaging has the potential to enhance the sensitivity and resolution, resulting in better disease diagnosis. Multifunctonal nanoparticles are, therefore, emerging as an interesting class of materials. Multifunctional nanoparticles with multiple capabilities (imaging, targeting and delivery) have potential in bio-labelling, MRI and drug delivery applications.
Accordingly there is a need for new hydrophilic nanomaterials for use as contrast agents in MRI and for labelling cells. Furthermore, there is a need for polymers that are hydrophilic, biodegradable, non-toxic and biocompatible, that can be used to impart these properties to nanomaterials. It would be a further advantage if such polymers could be prepared by environmentally friendly and economically inexpensive routes.